the GT3 motor does achieve more power with less displacement, but that's not what has been debated. the Carrera motors are what we're talking about here since they're at least in the same stratosphere in terms of price, and in fact they don't provide any more hp/liter than the S65. even the FI motors that premiered in 2009 (two years after the S65 did) provide just slightly less hp/liter than the S65, and they do so even with the benefit of direct injection.

345 hp / 3.6L = 95.8 hp/liter
385 hp / 3.8L = 101.3 hp/liter

414 hp / 4.0L = 103.5 hp/liter

clearly the GT3RS 4.0's 125 hp per liter (500 total) is in an entirely different league and quite an achievement, but again, considering the price tag on that, it's not worth debating.

as I said in my first post, the Carrera motors do win in terms of fuel efficiency. however, that trade-off is both unsurprising and well worth it when you consider the improved throttle response and flatter torque curve of the S65 (which is due in part to the individual TB's).

Here is a valid point. What are the crate costs of all these motors?

I know a 4.0 is quite expensive, but last I remember a 3.6/3.8 GT3 block isnt much difference in price AS A CRATE MOTOR compared to the S65. Both run about 30K IIRC.